Bituminous coating for timber



Patented June 15, 1943 2,322,105 BITUMINOUS COATING roa TIMBER Walter Paul Arnold, Orrville, Ohio, assignor, by mesne assignments, to Koppers' Company, a

corporation of Delaware No Drawing. Application July 15,1940

- Serial No. 345,674

9 Claims.

The present invention relates to the protection of wood and contemplates more especially the provision of simple method and means whereby the surfaces of timber can be furnished with a substantially continuous, water-repellent coating or sheathing of substantial thickness which is stably affixed to the timber andis especially adapted to impede the penetration, into the body thereof, of aqueous liquids wherein it may be immersed, thereby furnishing it with enhanced resistance to attack from waters containing injurious agents.

As a structural material in many of its applications wood is frequently employed in locations where it is in continuous contact with liquid water that harbors organisms destructive thereto and other agents which alter its chemical structure and promote deterioration of its woody fibers. Protection of wood against such destructive agents has in the past been primarily directed to simple impregnations of the woody structure both with inorganic and organic materials and combinations thereof. The employed methods of treatment as well as the characteristics of'the protecting media used have left the outer surfaces of the so-treated wood substantially unprotected save for the relatively tenuous films of preservative bodies left thereon by adsorption incidental to the processes of impregnating the deeper portions. Many of the generally employed preservative media are more or less soluble' in water and the thinlayer thereofon the treated timber can be quickly leached from the surface thus leaving this first point of attack by .destructive agents quite exposed to their action.

Two universally employed methods of treating wood for "its preservation with such relatively thinly liquid preservatives as creosote oils, aqueous solutions of fungicidal salts, and the like, are known in the art as the full-cell and the "empty-cell processes. In the former, the cells of the treated timber are left with a considerable content of the applied preservative which can thus migrate to the treated surface to replace that which is removed by such action as leaching, and the like; the quantity of such material thus stored in a treated timber is of course limited and is ultimately exhausted andat a rate depending upon the nature of the timbers environment which, if it happens to be a mobile liquid, can be rather rapid. In the latter process, i. e. the empty-cell, the cells of the treated timber are substantially emptied of, and its surface drained free from, the employed preservative before said timber is discharged from the process of treatment and with the result that its surface and its inner cell-walls are left with only a thin coating 'of absorbed preservative and little in the way of reserve content that can subsequently difiuse to the surface to replace losses thereof due to leaching and the like.

From the above-given it is manifest that the provision of simple and efiective method and means whereby timbers can be supplied with a durable covering that is of substantial thickness and imperviousness more especially to liquids in immediate contact therewith, will be an important aid in the preservation of wood and will enhance the effective life of leachable preservatives and timber fibers located beneath it.

An object of the present invention is therefore to furnish a cheap material and a method of applying the same to timbers whereby they can be provided with a relatively impervious, enveloping coating of substantial thickness that is sufiiciently pliable to withstand ordinary shock but is not tacky to touch and is adapted to serve as a protective layer between the body of the timber and a surrounding environment.

Another object of invention is the provision of bituminous materials whose properties are such that they are employable for the impregnation of wood in a one movement process and are adapted to leave on the so-treated wood a tenaciously attached and water-resistant sheathing that is continuous with and securely held by filaments of the bituminous materialconforming with and extending deeply into the interstices of the so-treated wood-structure.

"A further object of invention is to provide for the surfaces of timber that has been impregnated with such water-soluble fungicides as zinc chloride, mercury salts, and the like, improved protection against the leaching action of water thereby to prolong the effective action of such salts and in result the life of the timber.

A further object of invention is to furnish cheap and readily available materials that are employable within the limits of temperatures at which wood is safely treatable and are adapted to achieve the above-stated objects in equipment that is usually available in conventional woodpreserving plants and are compatible with woodpreservatives in general use in such installations, thereby avoiding the expense of special storage facilities and equipment for their handling.

A further object of the invention is to provide a product having the characteristics of the foregoing processes respectively.

The invention has for further objects such other improvements and such other operative advantages or results as may be found to obtain in the processes and product hereinafter described or claimed.

According to the present improvement in the preservation of wood and similar materials, they are provided with an external, continuous, and moisture-repellent layer'of substantial thickness by their treatment at elevated temperature, and preferably under pressure, with a bituminous material that is preferably derived from coal tar and exhibits, at a temperature to which wood can be safely elevated and at a reasonable pressure, sufflcient fluidity to penetrate the cellular structure of the wood a substantial depth below the surface and, at ordinary temperatures, the said bituminous material is sufficiently lacking in brittleness to resist, without cracking, ordinary handing and installation of the wood it covers, and yet is not tacky. As its temperature is reduced from that at which the wood is treated to atmospheric temperature, the preferred material shows in addition throughout substantially the entire range of cooling that relatively gradual increase in viscosity which is typical of liquids and is in sharp contrast to that exhibited by such substance, for example, as montan wax, and the lke, that changes abruptly within a short temperature range from a thin fluid to a brittle crystalline solid.

The last-named characteristic, 1. e. a relatively gradual change in viscosity over a wide range of temperature, is of decisive importance for the present purpose because such characteristic makes it feasible to inject at an elevated temperature into the Wood's cellular structure and to retain therein under-pressure a considerable quantity of the bituminous material and, thereafter, both by reduction of the pressure at the Wood's surface and by that feature of the presentimprovement comprising a gradual, controlled cooling appropriately correlated with viscositytemperature changes of the injected material, controllably to eject a portion of the same and at such rates of extrusion that the material coalesces and solidifies into a continuous highlyviscous surficial coating that is firmly attached to the timber by filaments of the material extending deeply into the irregularly-shaped openings of the cellular structure. Bituminous materials whose consistencies either change abruptly in a short range of temperature or alter relatively little over a wide range of temperature are not .suitable for the present use because either, re-

spectively, solidification thereof would take place within the wood too rapidly for an adequate extrusion to be brought about, or the viscosity of the extruded portion would be so low that the 88 C. its viscosity is between about 4 to 8 poises.

The method of employing a coal-tar derivative having the above-delineated properties will vary somewhat not only with the nature of the material that is to be treated but also with variations in the specific characteristics of the coating agent. According to the instant preferred procedure with the material having the said preferred characteristics, the charge of wood is placed in a pressuretreating cylinder, of any suitable type and the tarry coating-agent is introduced thereinto at a temperature of about 95 C. until said cylinder is substantially filled. Any loss in temperature of said coating-agent, in those instances where the wood is at a lower temperature than the treating agent, is compensated for as rapidly as possible and the charge of wood as well as the coal-tar derivative in which it is immersed are brought to a temperature of approximately 88 C. at which they are allowed to stand under atmospheric pressure for approximately 3 hours. The hydraulic pressure in the treating cylinder is then gradually increased by any suitable means until the pressure on the liquid coating-agent is approximately 150 pounds per' square inch thereby to force the latter into the cellular structure of the wood. After the wood has been so impregnated under pressure for approximately a three-hour period, the unabsorbed tarry coating-agent is withdrawn from the treating cylinder while still maintaining the impregnated timber under a pressure of approximately 150 pounds per square inch.

Thereafter the treated wood is gradually cooled in the treating cylinder at atmospheric pressure to a temperature of about 50 C. which is reached after approximately 12 hours whereupon the treated wood is removed from the cylinder with its surface covered with a continuous imperforate coating of substantial thickness of the bituminous material. In the above-described process that portion of the treating material that is injected by pressure into the cellular structure of the wood is retained therein under considerable pressure even after pressure conditions at the surface have been reduced to atmospheric, a significant lapse of time being required, because of the viscous nature of the injected material, for it to come into equilibrium with the reduced pressure conditions obtaining at the timber surface after the re- 4 moval of the excess of treating'material from the material would not accumulate into a layer of substantial thickness on the woody surfaces, but would drain therefrom.

In providing wood and similar substances with the water-repellent coating of the present improvement, there is preferably employed a coaltar product having a softening point, as determined by the cube-in-water method, of about 43 to 49 C. Upon distillation to a vapor temperature of 300 0., this coal-tar product shows a pitchy distillation residue of about 80% by weight, the softening point (cube-in-water method) of such residue being generally about 73 C. although in certain instances it may vary somewhat therefrom. At about 50 C. the preferred coal-tar product exhibits a viscosity of between about 500 to 1200 b01585 whereas at treating cylinder. By virtue of this differential pressure, a portion of the bituminous liquid is extruded to the surfaces from the innumerable cells extending deep into the structure of the wood, at a rate controllable by the rate and extent of cooling, and, upon reaching the surface, fuses into continuous enveloping sheathing that after reaching atmospheric temperature is closely bonded to the wood surface as an imperforate, non-tacky covering.

The proportion of extruded material to the total quantity thereof injected into the wood can be also controlled by varying the quantity of air imprisoned in the cellular structure before injecting the impregnating liquid thereinto; that is, the greater the volume of air pressed into the wood cells before the liquid is forced thereinto, the greater the volume of the injected liquid the air is able to displace to the surface during its subsequent expansion, other factors being equal.

formity in the water-repellent coating of timber by the invention, to carry out the extrusion and cooling step while maintaining a pressure in excess of rather than at atmospheric pressure during the same. As an example of operating according to this modification of the improvement the following is given: after sealing the tobe-treated timber in the treating cylinder compressed air was introduced thereinto until it reached a pressure of 20 pounds per square inch. A quantity of the above-described material derived from coal tar was pumped into the treating cylinder against this pressure until'the same was filled, the liquid pressure being thereafter raised to 175 pounds per square inch and the temperature increased to 88 C. The timber was soaked at this temperatur and pressure for about four hours. The excess of tarry material was then removed from the treating cylinder while maintaining an air pressure of 20 pounds per square inch therein which was also ,maintained during the cooling and extrusion period when the temperature was reduced from 88 to 50 C. The so-impregnated timber was then removed from the treating cylinder with a continuous coating varying from .03 to .06 inch in thickness.

It is not intended to limit the claimed imextrude as an adequate coating; therefore,-with woods of more open structure having larger cell-' openings it is highly desirableduring both the interval it is being separated from the treating bath and, thereafter, to retain super-atmospheric pressure on the timber until cooling has increased the viscosity to such point that when extrusion is started by release of external pressure, the coating-substance will not drain away but willbe retained on the surface. Along with the co-ordination of the rate of cooling and the pressure employed, the extrusive effects are further modifiable accordingly as the amount of air imprisoned in the wood is varied before imsome circumstances a partial vacuum at the provement to the specific procedures or condiv ing a high viscosity at atmospheric temperatures and sufiicient fluidity at temperatures which are not deleterious to the to-be-treated material, to

enter its cellular spaces in substantial quantity and there be retained under a head that is adequate, after removal of the impregnated material from a bath of said substance, to extrude a quantity of the same to the surface of the wood under conditions of cooling that are so correlated with its viscosity changes that upon issuance from the myriad of cell-openings there is no substantial drainage from the surface but instead coalescence into a continuous non-tacky coating firmly held by fibrils extending deeply into the woody structure.

The precise procedure in practicing the present process will naturally be varied in accordance with the cell structure of the to-be-coated material. In the case of a denser wood having small-sized cell-openings, higher pressure will be required to force the coating-substance deeply into its structure and because of the high resistance, they offer, a relatively longer time will elapse on release of the treatment-pressure before the substance thereby forced into the cells comes to equilibrium with pressure conditions obtaining at the wood surface; therefore, during the subsequent step of extrusion and cooling, any super-atmospheric pressure at the surface can be usually dispensed with. On the other hand, however, in the case of a Wood of relatively open structure, penetration of the wood will be ef-E fected with less pressure, but equilibrium between the pressure at the wood surface and that obtaining in the impregnated coating-substance will be established at the treating temperature so rapidly that insuflicient of said substance will Water Water absorbed absorbed in in untreated treated pine nine Pounds Found:

2 days l5 4 days. 19 3. 5 6 days. 2 4 8 days 23 4 14 days 24 4 timber surface will facilitate extrusion of the coating-substance'during that step.

The improvement of the instant invention thus provides'woody substances treated according to its process with twofold protection against the penetration of moisture; there being the external, imperforate coating that forms a barrier between its fibers and any surrounding environment as well as that quantity of the impregnating material which is not extruded from the cells and functions as a second line of defense in the event that the exterior coating is damaged for any reason. The new product is especially adapted for use in those places where a timber must be immersed in water and because of'the pitch-l ke nature of said coating it is also suitable for use as a structural material that is in direct contact with weaker solutions of alkalis and acids; for example, in the construction of tanks and the like.

The extent to which any timber is protected by the present improved process will depend in considerable measure on the quantity of bitu-. minous material that is injected into a unit,

thereof. Some protection will result with the retention of as little as 3 pounds per cubid foot. However, the preferred minimum is 6 pounds per cubic foot of the treated wood and approximately 10 pounds is recommended.

The following tabulation showing a comparison between the water-absorptive characteristics of untreated pine wood and the same wood that had been treated according to the present process is illustrative 0] its advantages. In both instances the treated and untreated pine were submerged in water the indicated number of: days during which they absorbed the stated pounds of water per cubic foot of material:

. timber. was still absorbing' water to a slight extent,whereas in the case of the treated pine equi be retained during removal from the bath to -75 librium had been reached on the sixth day.

Amongst other compounds, such water-soluble substances as zinc chloride, mercury bichloride and sodium fluoride are well-known in the woodpreserving art in which they have been advantageously employed as fungicides, insecticides,

and the like. Timbers that are impregnated solely withsuch materials have the disadvantage that the protective substance is relatively rapidly leached especially from their surfaces which are naturally the first points of attack of fungi and of other destructive agents, and they are consequently not adapted for exposure in marine positions. Wood, that has been previously treated for its protection with such watersoluble salts, can now be successfully sheathed with a waterrepellent coating according to the present process, with the result that the effective life of protection provided by such salts is greatly extended and timbers in which they are used as the preservative are employable under conditions previously thought impractical.

Although the bituminous material hereinabove specified in connection with the description of the present improvement has its origin preferably in tarry constituents obtained by the distillation of coal in order to take advantage of known fungicidal and insecticidal properties of compounds contained therein and the presence of which in the water-repellent coating formed from such material serves as additional protection, it will be obvious to those skilled in the art that bituminous material of other origin that conforms substantially to the specified characteristics is adapted for use in the present process.

An important advantage of the water-repellent coating resides in its tendency to seal up checks and fissures in the timber to which it is applied thereby closing breaks in the continuity of its surface that occasionally penetrate deeply into the interior. In that the coating formed by the preferred material has some measure of plasticity it is able to yield. without development of cracks, to expansions and contractions of the timber it covers and to adjust itself to changes in dimensions of checks therein, thus tending to maintain the covering continuous at all times.

The invention as hereinabove set forth is embodied in particular form and manner but may be variously embodied within the scope of the claims hereinafter made.

I claim:

1. In the art of providing wood, and the like, with a substantially continuous, moisture-repellent coating of a bituminous liquid that is highly viscous at ordinary temperatures, the steps comprising: impregnating such material to a substantial depth with the bituminous liquid by means of pressure on the bituminous liquid in contact with the material and thereby confining within its cellular structure an ejectable quantity thereof that is at least adequate to coat its exterior surface; removing the so-impregnated material from contact with excess of said liquid; reducing the external pressure on the material to allow the soimpregnated liquid to extrude from said materials cellular structure onto its surface; and during the extrusion subjecting the surface of the material to a gradual cooling so correlated with respect to, the gradual viscosity change of said liquid resulting from its gradual drop in temperature as to effect its coalescence over the materials surface and its retention thereon as a substantially continuous non-tacky surface 'coating that is pliable to withstand ordinary shock, by

gradually increasing its viscosity on the surface of the material to correspond with the gradual increase in viscosity typical of the liiquid over the range of cooling.

2. In the art of providing wood, and the like, with a substantially continuous, moisture-repellent coating of a bituminous liquid that is highly viscous at ordinary temperatures, the steps comprising: impregnating such material to a substantial depth and at an elevated temperature with the bituminous liquid by means of pressure on the bituminous liquid in contact with the material and thereby confining within its cellular structure an ejectable quantity thereof that is at least adequate to coat its exterior surface; removing the so-impregnated material from contact with excess of said liquid while maintaining the former at an elevated temperature; reducing the external pressure on the material to allow the so-impregnated liquid to extrude from said material's cellular structure onto its surface; and during the extrusion subjecting the surface of the material to a gradual cooling so correlated with the viscosity change of said liquid resulting from its gradual drop in temperature as to effect its coalescence over the material's surface and its retention thereon as a substantially continuous non-tacky surface coating that is pliable to withstand ordinary shock.-

3. In the art of providing wood, and the like, with a substantially continuous, moisture-repellent coating of a bituminous liquid, the steps comprising: impregnating such material at about C. to a substantial depth with a hydrocarbonaceous liquid having a viscosity at about 50 C. of the order of about 500 to 1200 poises by means of pressure on the bituminous liquid in contact with the material and thereby confining within the cellular structure an ejectable quantity of said liquid that is at least adequate to coat its'exterior surface; removing the so impregnated material from contact with excess of said liquid while maintaining the same at an elevated temperature and pressure; reducing the external pressure on the material to a lesser-surface pressure to allow the so-impregnated liquidto extrude from said material's cellular structure onto its surface; and during the extrusion subjecting the surface of the material to a gradual cooling so correlated with the viscosity change of said liquid resulting from its gradual drop in temperature as to effect its coalescence over the material's surface and its retention thereon as a substantially continuous non-tacky surface coating that is pliable to withstand ordinary shock, by gradually increasing its viscosity on the surface of the material to correspond with the gradual increase in viscosity typical of the liquid over the range of cooling.

4. In the art of providing wood, and the like, with a substantially continuous moisture-repellent coating, the steps comprising: impregnating the wood to a substantial depth and at a temperature of about 90 C. with a bituminous liquid, under a pressure of at least pounds per square inch, that is derived from coal-tar and exhibits at 50 C. a viscosity of the order of about 500 to 1200 poises and at about 90 C. a viscosity of about 4 to 8 poises, by means of pressure on the bituminous liquid in contact with the material and thereby confining within the material's cellular structure an ejectable quantity of said liquid that is at least adequate to coat the exterior surface of said material; removing the so-impregnated material from contact with an excess of said liquid at an elevated temperature; reducing the pressure on the surface of said impregnated material to allow the bituminous liquid to extrude from the cellular structure thereof;

. and during the extrusion subjecting the surface of the material to a gradual cooling so correlated with the viscosity change of said liquid resulting from its gradual drop in temperature as to effect its coalescence over the material's surface and its retention thereon as a substantially continuous non-tacky surface coating that is pliable to withstand ordinary shock by gradually increasing its viscosity on the surface of the material in the order of 4 to 8 poises to 500 to 1200 poises.

5. In the art of treating wood, and the like, for its preservation, the steps comprising: depositing in the inner structure of said material a substance that is leachable therefrom by water and is adapted to improve its resistance to decay; thereafter providing the so-treated material with a substantially continuous, moisture-repellent coating to prolong the effective life of said waterleachable substance therein, by steps comprising;

face; and during the extrusion subjecting the surface of the material to a gradual cooling so.

correlated with the viscosity change of said liquid resulting from its gradual drop in temperature as to effect its coalescence over the material's surface-and its retention thereon as a substantially continuous non-tacky surface coating that is pliable to withstand ordinary shock, by gradually increasing its viscosity on the surface of the material to correspond with the gradual increase in viscosity typical of the liquid over the range of cooling.

6. In the art of protecting wood, and like material, for its preservation, said material containing in the structure thereof a water-leachable substance adapted to enhance its resistance to decay, providing said material with a substantially continuous, moisture-repellent coating of a bituminous liquid that is highly viscousat ordinary temperatures by steps comprising: impregnating said material to a substantial depth and at an elevated temperature with said liquid by means of pressure on the bituminous liquid in contact with the material and thereby confining within its cellular structure an ejectable quantity thereof that is at least adequate to-coat its exterior surface; removing the so-impregnated material from contact with excess of said liquid at an elevated temperature; reducing the external pressure on the material to allow the so-impregnated liquid to extrude from said material's cellular structure onto its surface: and during the extrusion subjecting the surface of the material to a gradual cooling so correlated with the viscosity change ofsaid liquidresulting from the gradual drop in temperature as to eil'ect. its coalescence over the materials surface and. its retention thereon as a substantially continuous non-tacky surface coating that is pliable to withstand ordinary shock, by gradually increasing its viscosity on the surface of the material to correspond with the gradual increase in viscosity typi-- cal of the liquid over the range of cooling.

7. An article of the character described and comprising wood, 01' the like, having a highlyviscous, water-repellent and substantially continuous coating of a bituminous liquidaffixed thereto by a myriad of filaments of the same material extending deeply into the cellular structure of said material-from which the said coatin has been extruded, said coating having the properties and characteristics of a liquid bituminous material first impregnated under pressure while liquid and then allowed to extrude by release of the impregnating pressure, with cooling of ,the

extruded liquid on the surface of the wood as it exudes under controlled cooling graduated to correspond with the viscosity change of said liquid resulting from the gradual drop in temperature as to effect its coalescence over the materials surface and its retention thereon as a substantially continuous non-tacky surface coating.

8. An article of the character described and comprising wood having deposited in'the cellular structure thereof a water-leachable substance adapted to improve its resistance to decay and on its surface a highly-viscous, water-repellent and substantially continuous coating of a bituminous liquid aflixed thereto by a myriad of filaments of the same material extending deeply into the cellular structure of said material from which the said coating has been extruded, said coating having the properties and characteristics of a liquid bituminous material first impregnated under pressure while liquid and then allowed to extrude by release of the impregnating pressure, with cooling of the extruded liquid on-the surface of the wood as it exudes under controlled cooling graduated to correspond with the viscosity change of said liquid resulting from the gradual drop in temperature as effect its coalescence over the material's surface and its retention thereon as a substantially continuous non-tacky surface coating.

9. In the art of providing wood, and the like,

with a substantially continuous, moisture-repellent coating of a bituminous liquid that is highly viscous at ordinary temperatures, the steps comprising: storing within the cellular structure of said wood at an elevated temperature and pres.-

sure a quantity of said bituminous liquid, reducing the external pressure on the material to allow a portion ofsaid liquid to extrude to the surface of the wood and during the extrusion subjecting the surface of the material to a gradual cooling and pressure-release graduted to prevent ejaculation of the so-stored liquid from cellular structure while allowing its extrusion to and coalescence over the wood's surface and its retention thereon as a substantially continuous non-tacky surface coating that is pliable to withstand ordinary shock, by gradually increasing its viscosity on the surface of the material to correspond with the gradual increase in viscosity typical of the liquid over the range of cooling.

v WALTER PAUL ARNOLD. 

